A respectful Korean term used by females to call older males such as older male friends or older brothers, but now with the Hallyu kickin' in, people are using it being as annoying as the Japanese, "Kawaii" wave.

Oppa is a term that is used in Korean by a girl to call a man who is older than her, but by less then about 10 years. It is a term used traditionally in respect to ones elders
An oppa can be an:
Real biological older brother
A male friend who is older than the woman
An older male a girl is trying to flirt with

" sang chan please help me to put on this band aid"
"Ye Jin ah! How dare you speak my name"